Question on which NIM amp for a 3He detector?

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Dennis P Brown
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Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

I decided to upgrade to a complete NIM system for neutron detection with my 3He tube. I ordered a NIM box, a HV power supply (0-5 kV) and a rate counter but have no idea which course amplifier is a better 'fit' (I have a self powered pre-amp already.) Which of these make the most sense for a system? A few words on how they differ would be useful, too:

TENNELEC TC 246 AMP/SCA COARSE GAIN MODULE
or
TENNELEC TC265A LOW/WIDE AMP/SCA NIM BIN PLUG IN (op & service manual available)

or(maybe not a proper amplifier(?))
Ortec Delay Line Amplifier Nim Bin Module Model 460

All are on Ebay, of course. Appreciate any input
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Re: Question on which NIM amp for a 3He detector?

Post by Alex Aitken »

The TC246 has a spectroscopy (shaping) amplifier, so that ought to work well. A give away for these devices is a knob to change the shaping time. Some of these will go from 100ns to 10us in 5 or so steps. Each setting is a different trade off between voltage noise and current noise. Be aware they often have two sets of numbers, one double the others. This is not extended range, but a different way of measuring the time. A bit like the Peak Music Power Output scam for speakers.

The TC265A does not seem to be a spectroscopy amplifier. Amp/Discriminator.

The ORTEC model 460 is a spectroscopy amplifier, but the method it uses is different. It's manual suggests it's designed for scintillation detectors. Probably best to give this one a miss.

I may be talking rubbish, but I think I've read that Tennelec and Canberra 9pin preamp connectors have different pin outs.

It's difficult to know with these things when you are buying a 50 year old card. I've recently bought some NIMs and am looking at some others but there are a few pitfalls. My mini bin has no access or space at the back which means NIMs with connectors on the back don't fit, and (I think) no 115vac which some cards need. I would look at the TC246 but also consider other models, hopefully other members will have experience.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

That is certainly helpful and very informative, too. Thanks' Alex.
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Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Alex is correct. In an abortive effort to keep the preamps and NIM bin coarse amps "in-house" Tennelec did indeed screw with their 9 pin preamp power plugs. This aced out what was a defacto standard for this plug. I imagine after some one bought their preamp and plugged it into there Ortec Nim amp and perhaps blowing up the Tennelec preamp, they got wise and went back to standard 9 pin power configuration. So.........any use of anything Tennelec that you buy be it a preamp or a bin mount amp, where you will need to use the 9 pin for power you need to tear into it and figure out the wiring for the voltages and ground.

You are in luck.
I have the pinouts and they are as below

Stock Ortec 9 pin industry standard more or less
Note: the +/-6volt buss is just never used much anymore. 95% of all modern bins, while all are buss wired for it, do not ever power it up from the main bin supply. Heavy 2-3 slot +/- switchable nim bin plugins tend to power up this 6 volt buss using the 120vac buss to power this plugin supply to activate the 6 volt buss.

1 ground
2 ground
3 +6v
4 +12v
5 -6v
6 -24v
7 +24v
8 n/c
9 -12v

Tennelec oddball 9 pin (not on all tennelec) However this was their pin-out on their TC203 as noodled out by me... they used only +/-12v
Again, you must open the Tennelec preamp or plug-in amp to be sure. The easy check is to put an ohmmeter on the case or chassis and then probe pins 1 and 2. These should be shorted to ground if it is a standard Ortec compatible.

1 P/Z in
2 n/c
3 +12v
4 Preamp test in
5 Detector bias
6 Ground?
7 n/c
8 -12v
9 ground

Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

I checked my old win98 computer. I used this in the late 90's when just getting into NIM and found an image of the TC203 that I bought off e-bay and my neophyte write up on it from back then. You definitely needed their preamp. I attach the info. The ancient word file was converted to PDF and the fonts are weird from the original, but very readable.

At the time, this was a really sweet amp. The adroit could easily turn the 9 pin to a compatible.

Richard Hull
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tc203blr.JPG
TC203BLR.pdf
(131.23 KiB) Downloaded 30 times
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Thanks Richard for the excellent information - needless to say, not exactly available anywhere else.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Here is a question on the NIM box and what it does - you provide pin read outs with voltages for the given pins, so if one provides those voltages to the pins in a given NIM application device, then it should power up and operate (if working)? I'm asking because one of the application devices arrived but the NIM box hasn't and isn't likely for a week or more. So, I'd like to test it at some point maybe sooner rather than later and if there are issues, able to return it before the return time lapses.
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Re: Question on which NIM amp for a 3He detector?

Post by Alex Aitken »

Depending on the unit, it could be using +24 +12 +6 -6 -12 -24 ~117 or +200. I understand 200v is rarely supported or used, a lot of pulse testing stuff seems to sync to 117 to reduce noise but probably nothing needed for spectroscopy. You could check the back of your NIM to see what is used, and I've done this a lot just to see what will work. My 35+ has a NIM slot and I think more voltages are supported than in my bin. An 8075 hit my door mat today and it uses all but 1 of the low voltages. I'd wait for the bin to come, and I'd check the lines levels are right and clean before plugging anything in.
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Both the bins and all modules are easily checked for what voltages are their in the case of the bin. No bin is even needed to determine what any plug in needs to function.

Take one side or the other off of the plug-in NIM module. Look at the power end of the plug internal NIM power connections to see what wires exit the plug and run to the electronics card. Rarely, in some cases, at the base of the faceplate of the module, the power requirements are clearly printed with the voltages needed and the current ratings or "draw" in that supply.

It is automatically assumed that if you own a NIM bin or modules that you have a full diagram of the NIM power plug buss system. without it you are adrift in a sea of calamity.

Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Both the bins and all modules are easily checked for what voltages are their in the case of the bin. No bin is even needed to determine what any plug in needs to function.

Take one side or the other off of the plug-in NIM module. Look at the power end of the plug internal NIM power connections to see what wires exit the plug and run to the electronics card. Rarely, in some cases, at the base of the faceplate of the module, the power requirements are clearly printed with the voltages needed and the current ratings or "draw" in that supply. (photo supplied below)

It is automatically assumed that if you own a NIM bin or modules that you have a full diagram of the NIM power plug buss system. Without it you are adrift in a sea of calamity. (diagram below)

Often modules that are whole within themselves will only have a few gold pins in their NIM connector.
Look there into its plug to see what power is really needed, using the supplied pin-out diagram.

Richard Hull
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Notice the top of the plug is for DC power and the bottom of the plug is for 120volt AC buss power to modules using a power trnasformer internal to the module.
Notice the top of the plug is for DC power and the bottom of the plug is for 120volt AC buss power to modules using a power trnasformer internal to the module.
Carefully enlarge this image by clicking on it and read all the power requirements fully printed in the lower right corner along with current draws.  AC means there is a power transformer in it that uses the NIM AC power buss.  It still used buss power of +12 and -12 volts as well. the Ortec log/lin to the left also has its power needs printed out on it.
Carefully enlarge this image by clicking on it and read all the power requirements fully printed in the lower right corner along with current draws. AC means there is a power transformer in it that uses the NIM AC power buss. It still used buss power of +12 and -12 volts as well. the Ortec log/lin to the left also has its power needs printed out on it.
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Fusion is the energy of the future....and it always will be
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Thank you Richard and Alex. Being new and certainly never having really seen a NIM in any detail, this is all rather strange. I understand the need for a NIM HV module (and assorted cables - ugh; too many types, now I need to order another), a NIM case to hold/power these modules, a pre -amp (for the 3He tube; and thank you Richard for locating that on Amazon), a NIM based Amplifier, and a scalable counter. However, Richard's Timer/multi-scaler in his NIM box is unknown to me. Exactly what is that and what is its purpose in a detector system?
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Remember the NIM system is a nuclear physics electronic Erector set. Kids with this NIM Erector set (Mechano for the euros), are expected to make anything the mind might imagine, nuclear instrument wise. If you detect something like a pulse that is recurring via pre-amplification, discriminating, shaping, amplifying, it just might be nice to be able to count say a million or more of these pulses a minute or 149 pulses over 24 hours.

This is the use for this module. To receive pulses, count and display them over any user selectable time period. In the case presented in the preceding image, a fist sized piece of U ore was placed under a 2" pancake GM tube powered to a set voltage of 900 volts using a NIM bias set module. The signal for each pulse from the tube is fed to a NIM coarse amplifier module where it is amplified and clipped to a fixed voltage. It is then massaged to a specific shape with another NIM module. This nice clean signal is then sent to an analog ratemeter module with a meter and then onto a digital ratemeter/Timer NIM module set to count for one minute and stop. This has been done and the piece registers an inaccurate emission rate from the exposed surface of the U ore rock of over 226,000 particle detections 1 cm distant from the pancake probe over a 60 sec time period.

Inaccurate, I say, as the pancake will detect only surface alphas to about 70%, Near surface betas to 85%, and gammas from varying depths to under 5%. In addition there are pulses lost or not counted over that one minute count time due to "pile-up", not accounted for. My hand that placed the rock under the pancake suffered a far greater maelstrom of particles than this per unit time from this bland and un-impressive rock.

Thus, the industry making NIM modules has long ago figured out just the right modules to make my custom GM counter in their erector set toy nuclear building block structures. It was up to me to put them in order and tune them up. The counter/timer/rate meter module was my optical readout amid a mass of electronic signals originating in the pancake GM detector.

This same NIM toy module could have been used by the adroit hand armed with a myriad of other NIM toy modules to count neutrons from a BF3 tube, an 3He tube or a PMT with proper scintillator.

With the introduction of a simple single channel analyzer NIM module placed in my GM chain above, had I used the sodium iodide PMT detector instead of the above GM pancake, I could have easily counted only the 610 KEV gamma emission from the rock's contained Bismuth 214, radium daughter.

I have many NIM bins and many modules. I supply a simple early image of this one specific system setup looking at a very weak U ore sample.

Nice to have a bunch of NIM toy modules if you are doing nuclear measurements.


Richard Hull
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Early 2005 NIM setup to catagorize my specimens from a U hunt in Utah of that year.
Early 2005 NIM setup to catagorize my specimens from a U hunt in Utah of that year.
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Re: Question on which NIM amp for a 3He detector?

Post by Rex Allers »

I don't have any NIM stuff here, myself, but I found Richard's post of the NIM connector pin-outs a good reference to save. But it prompted me to look a bit more.

Looked for the image source and found it in:
https://www.osti.gov/servlets/purl/7120327
(page 25)

This is a scan of a NIM Standard document from 1990

Richard's shared image is a bit truncated at the bottom.
Both versions suffer from some noise (dark speckles) in the scan of the original paper document.

I extracted a new image from that 1990 document and spent some effort cleaning away most of the visual speckles. So I made a PNG version that is a little more complete of the original and hopefully a little easier to read with the clean-up.

'NIM Conns 1990.png'
NIM Conns 1990.png

Then I searched hoping to find a similar document that was already cleaned up.

I found one in document from a German company here:
https://www.fastcomtec.com/ftp/manuals/nim7022-7033.pdf

(called Page 12 but actually page 7 of the 8-page PDF)

I have extraced it as:
NIM Conns 2.png
NIM Conns 2.png


This one was clean without any image editing. It also has a few more pin functions defined than were in the original from 1990.

Since most modules only use a small subset of the connector pins, it is unlikely that we amateurs will find newer modules that use these additional pin definitions. But I thought it was good to see this newer connector specification page.

------
So as I said, I have no direct experience with NIM stuff. Does this look good and helpful?
Should I post it again in the NIM FAQ Richard started and recently bumped up with an edit?
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Thanks Alex for this further work, I've made print outs. These are extremely useful to both ID pins but aslo if one needs to setup a module w/o a NIM box
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Re: Question on which NIM amp for a 3He detector?

Post by Alex Aitken »

It's Rex, not me! :)

Thanks Richard and Rex for the info. Due to lack of experience with NIMs I took a back seat. My Canberra card has no power markings but my Tennelecs do and this seems the norm for other big brands. I've probably stared at the connector in a dozen ebay listings and completely missed the writing on the front. *red face*.

I had cause to take the back off my bin, and most of the power lines come from what looks like a 1980's switch mode supply. Something of a nightmare. The -24v line is provided by it's own transformer board with a linear regulator and a big cap. There is no AC or high voltage at all into the back-plane. The 6v and -6v lines are 5v and -5v deliberately. Makes me wonder if that is going to be a problem. I'm wondering if it is possible to get the metal pins for the connector housing and retrofit AC from a step down transformer. I'm also wondering if cards that expect to draw 6v, say to generate 5v logic internally will fail to work. I looked at the power supply wondering if I could tweak the voltage, and though it is producing 5 voltages it has a bank of only 4 linear pots.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Oops, well, thanks to both Rex and Richard. These posts are great and really are giving me insight about NIM's (I didn't know what that that acronym even stood for ... .) I very much want to look at the insides of the NIM main box when it arrives and get a feel for its mode of operation. Certainly I do need to test the NIM modules I purchased and only a few days ago realized I didn't have all the required/correct HV cables for the PS module to connect to the pre-amp (I do have the correct ones for the 3He detector to the pre-amp) - the various flavors of those cables one could write a number of posts on. All part of the NIM experience, I guess.

I printed those NIM posts maps out and will mount them in my lab room. Those posts should get their own FAQ entry.

I am finally upgrading the pre-amp to 3kV caps as Richard suggested. I am considering a full wav single stage voltage multiplier for the transformer but that, if I ever move it forward, will get its own post. Diodes are my limiting factor.
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

I went back to my NIM FAQ of 2001 and added the pinout page above to the FAQ. So it is OK as originally written with the new included diagram pinout.
For those old and new alike who would know NIM check out the updated FAQ located at...

viewtopic.php?t=5107

You will find a lot in this FAQ in the form of multiple responses that add to it.



Regarding 6v lines....Forget they exist! In my new homebrew NIM supply work posted recently at.....

viewtopic.php?t=14544

I am currently planning on putting +/- 5volts on those buss lines. (brings NIM into the TTL and 5 volt electronics world of the 1970-2000 range of electronics for homemade NIM modules.) For some strange reason NIM modules using only discrete components were manufactured into the 1990's!!!
In many cases, I realize, OP amps that could replace 10 transistors were not all that fast compared to well designed discrete electronics. Add to this, the signal levels were originally designed when none of this IC stuff was around. Manufacturers were forced to live up to the old standards if they wished to remain module compatible across other manufacturers modules.

My supply, as I note, will be to design my own modules with all modern circuitry in them. +/- 5 volts is a must. Placing a simple power diode or two in series with a normal bin's +6 volt line, within my homemade module would make my 5volt TTL work fine. Another option is that my module could use the +12 volt NIM buss line to feed a linear 5 volt regulator within my module. Although it would be a waste of 12 volt power in the 5 volt regulator under nominally heavy +5 volt demands.

Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Finn Hammer »

Richard,

If voltage drop related losses in your linear regulator is your worry, try this little component:


https://www.mouser.dk/ProductDetail/REC ... 5HVA%3D%3D


It is a switcher, with neglectible losses.

Cheers, Finn Hammer
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Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Actually I own 5 of those tiny little buck regulators from Marlin P Jones and 5 similar boost regulators. I will try one of them. However, they are all positive boost and buck. and the NIM ground buss might not like flipping them for negative regulation. Always flys in the ointment.

https://www.mpja.com/Adjustable-15-37V- ... /30149+PS/

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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Since the NIM box came in, and is one of the reasons I started this thread, I have a few questions.

The NIM box appears to work fairly well (it was sold as non-functional since the power cord was cut off. See pic.) The unit provides +/-24 and +/-12 volts but the +/- 6 volts doesn't seem to be working. May or may not be important for other modules.

I installed the HV output module (unit on far left; bought separately) and that works - I used both a HV probe and a multimeter to read its output. It covers 5 KV range (neg.)

So I assume it has an internal switch for positive since the unit has lights for neg./pos. polarity - in any case, I assume the negative is what detectors use?

Also, the NIM box has a digital (ancient red diode array display) display module that measures either Hz or kHz (has a switch). On the back is a micro-coaxial connector. Again, not clear on what that unit is useful for? Guess I can hook up a signal to it and see if it reads kHz/Hz. But why would one care enough to build such a one-trick pony?

Finally, a "Delay generator" was included in something else I bought - what use is a delay generator? That is, is it of any use for neutron or x-ray detection? Kinda curious.

Meanwhile, I will be waiting for the amp and counter modules. Also, another HV coaxial cable in order to enable hooking up my pre-amp to the 3He detector. Only then can I try real testing to see what is involved with trying to operate these rather complex but interesting units.

As an aside, check the vacuum in my fusor chamber - reading 7.5 torr after two months with no pumping. For those that wonder about the issue of a slow leak compared to out gassing - this is a good example of the later. My chamber rises a few microns a minute when the pump is closed off but that rate slows rapidly. That is a sign of out gassing. A leak would continue and raise the pressure back to atmosphere (or close to it in a rather quick manner.
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Re: Question on which NIM amp for a 3He detector?

Post by Liam David »

One of the three switching power supply modules is likely busted. It could be dead electrolytics as that's what temporarily killed my crate. Crates usually get a little toasty while running and even high-temp-rated caps often don't survive 40 years like that. It could also be the (SCRs?) or bridge rectifiers on the back heatsink if someone plugged HV into the wrong port.

Most detectors take positive HV. Yours was likely hooked up to an HPGe detector, which typically uses around -4500V. There should be an internal switch or swappable jumper that's listed in the manual. the Nuclear Physics Lab website by Tim Koeth et. al. has a bunch of NIM manuals assembled.

You won't have any use for a delay line unless you're doing coincidence or other time-sensitive stuff.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Thanks, Liam. Got a feeling that the jumper is well marked. I should check it tonight. Didn't know which polarity detectors tended to use. Used many detectors over the years but all were black boxes and have never considered that question till now. Again, thank you.

Electrolytic caps do tend to leak and fail with age; that is an easy check. Pulled the schematics off the web so guess I'll do the diagnostics if any of my not yet delivered units require +/- 6 volts. Likely one will ... ;)

Richard's voltage supply seems far easier to install then any difficult tracing; if the issue isn't obvious, think I'll just order those.

Update: checked the module and yes it had a very simple jumper/bus 'bar' assembly (a mini-circuit board) that just had to be moved to engage the HV positive. See photo's. To say well marked is an understatement; even had instructions and arrows printed on it. They certainly understand scientist ;)
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Complete circuit board (Reset)
Complete circuit board (Reset)
Close up of "Bus Bar" (reset)
Close up of "Bus Bar" (reset)
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Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Note: 95 % of all NIM bins that show a +/- 6 volt test points DO NOT have +/- 6v capability built into their power supplies. I have harped on this for years! Plus and minus 6 volts is as dead as a doornail. Intrinsically a dead duck. 100% of all bins are bus wired for it though. If you want or really need + or - 6v you will have to buy or manufacture a 6 volt plug in module to power the buss. That ancient 6 volt buss was so dead that many manufacturers made it a special order supply item. They did start to manufacture nice plug in 6 volt high current plugin modules to power the bus. As it is hyper rare to find a module ever manufactured to use both the plus and minus 6 volt lines, The 6 volt plug in modules have a polarity flipper board if you have a module that demands only one of the 6 volt buss lines. I own a couple of these heavy two slot 6 volt modules.

90% of all HV bias supplies have an internal polarity flipper board in them. Most are set for positive from the factory. Again, all of this is noted in the original FAQ


I really hate to have to continually write all of this 6 volt and HV polarity flipper board data over and over again.

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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Getting the unit I first down loaded a schematic of the 402A unit's power supply and of course, it shows +/-6 volts in the schematic; however, if I had looked the unit over carefully, I would have seen a placard on the unit stated clearly stating it supplied +/- 12 and 24 volts. You'd think I'd read the FAQ's first ... but no.

Well, it is fun learning about these fascinating units and now having read the FAQ's I have a bit better understanding.
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

If one obtains a powered NIM bin in which the +/-6 volts are supplied within the supply, one may consider oneself most blessed among men. Whoever originally ordered it paid the long buck for that option to power a dead, early standard.

I have only one single module that gobbles up 4 slots and demands NIM +6 v along with +12 volts and the AC mains. It is an ancient Victoreen/Tullamore counter/scaler with preset. It uses six rows of lamps requiring the user to read the final count in BCD. The back panel has a slew of BNC plugs for gates, inputs and outputs, remote operations plug, etc. Inside this piece of cutting edge 60's technology are 6 large, full size electronic PC boards with hundreds of transistors festooned in row after row to obtain the number of J-flipflops and individual diode logic gates and buffering to light the 30 incandescent lamps in a BCD sequence counter. The preset switches have 60 wires scattered like spider webs going to the boards with associated halt gated diode logic matrix. What a piece of individual, hard wired art, miniaturized into a rectangular solid using the new fangled 60's printed circuit technology!

Yes! it works perfectly. I won't sell it, or use it. Its value is in passing it around for a "show and tell" over a crackling campfire while regaling tales of yore as beer and hot dogs are consumed, to the amazement of all assembled.

Ah...Th' good ole daze....

Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Richard, that unit looks a lot like a modernized "Ultra" code machine.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

The TENNELEC TC 246 AMP/SCA COARSE GAIN MODULE arrived today and when tested in the NIM box, promptly blew the 3 amp fuse - that's a lot of power so it has a serious short in that black box - that is a definite no go for that unit. So, have to return it.

Likely its one of their special units that does not work with a std NIM box. I noticed it had about 25 pins on its back - that NIM box doesn't support that number of pins so likely a few of those extra pins caused the shorting to ground. Guessing it has so many pins on that module to only be used in their special NIM box.

Guess I'll look inside to see what caused the issue and see if the device (likely) connects the 120 AC to something it most certainly shouldn't.

Update - yes, 90% of those pins have no use in my unit; however, the 246 does have a pin for the 117 AC line and in the unit that has a green wire that goes directly to ground via the module case! They certainly made sure that if you use any box but their's, then that NIM box's fuse is toast! So, makes sense they have all those useless pins and then designed one so it guarantee's via the NIM std to kill the box - they had class (mis)management back then - no wonder they were bought out.

Worse part, this unit was tested and certified by the seller as working (which I don't doubt - they didn't use NIM boxes but connected via cables so they'd never see that fatal issue with the design) - I'll let them know; maybe if that 117 service was removed it might work but not gonna test that. Not my job.

Update: the company wants the unit returned and will refund (with shipping costs) the price. They were very helpful and intend to test their other units to see if the #33 pin also is shorted on those units. So they can flag them and not cause issues. They were rather interested in the NIM information you guys provided to me about Tennelec and their amps not always being std NIM compliant.
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Pin 33 to case ground!! That is unbelievable. What a dastardly thing to do. Are you positive it is pin #33??

All stock NIM bins only have 10 pins in their back plane buss wired. Period! Thus, any folks making a custom module loaded with other pins are free to use any free pins for any reason to talk to their other custom plug ins. Thus, if your module has 21 pins poking out the the back of it....No problem! It will not blow the fuse in the bin! Why? ...The power buss lines are sacrosanct if you want to sell your module for future general use.

Again, I could design a custom SCA NIM module that will talk to 4 other modules that I make as a grouped effort. I use a lot of those reserved pins to chat with my other modules. However being smart, I also place regular BNC in and out plugs so it will also stand alone for anyone using a stock NIM bin. Naturally, I would have to wire a custom bin with all the reserve pins running across the buss and sell the bin with my modules as a plug and play NIM system.

Later, if the bin I custom wired is surplused without my 4 custom modules, it is still a fully functional stock NIM bin! The same goes for all my 4 custom modules, they are good to go individually, but instead of them not having those reserved pins wired, they will still live a happy life in a stock bin doing their individual thing they were created for. However, they will have to be externally jacked in via BNC plugs just like any normal NIM module. All of my custom pins in the module now just slip into dead holes in a normal bin.

I would never tie 120 volts (Pin 33) of a my custom module to ground to deliberately blow a bin fuse in an effort thwart any of my custom modules having a future use.

Stupid, stupid, stupid...

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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Whoa there Nellie!! I owned a 246 module, tested it and used it in a normal bin!!! I have it on my inventory list. I also have the data sheets! (Attached) It is a normal module!!

Note: ON the second page cut sheet. They say this 9 pin preamp plug will work with any other manufacturer's preamp! this means this module is fully compatible with normal 9 pin wiring. They note and warn that earlier Tennelec preamps MUST have a special power module purchase to function.

If the real pin 33 is connected to the chassis that is an after market issue. Please look at the plug again. It can be easily misread as the pin numbering manner is stupid and odd ball and I have trouble with it to this day! I fear to are seeing the buss AC ground pin #42 which is always green within the modules going to ground. As this module doesn't even use 120 volts for power the other two pins near ground 41 neutral, and 33 hot are either not there or are not connected! They are all jammed together at the base of the NIM plug. I think you are misreading. Every NIM module has a green wire from #42 to the modules metal case.

Again I owned this very module and verified it in a normal bin!! I am sure that due to its great value to NIM people who have picked over and purchased from my many NIM modules at HEAS for the past 10 years that it sold to someone. I haven't heard anyone complain.

Check it over again.

I am positive you have a dead shorted tantalum cap on one of the DC power lines I could fix it in 5 minutes, but send it back.

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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

I double and triple checked this issue and it was the 117 AC plug (#33) in the NIM connector and the module connector that mated with that specific pin went to ground in the unit. Again, I looked inside the case and that pin was affixed to a green wire and appeared factory installed. The green wire even had a proper "eye" connector soldered to the wire that was bolted to the case! There was no 'after market' appearances to that bundle or solder joint.

I agree the other pins make sense in light of your post - now I'm wondering if I had simply cut that green wire in the module then the unit would work fine, maybe? I will likely talk more to the company (they have three units besides this one.) As per an earlier post, I was warned some of these Tennelec amp units would blow other devices apparently in their misguided attempt to sell only their units bundled to their NIM system, maybe? But to ground a hot 117 AC line is beyond the pale, I'd think.

Maybe mine was modified by someone for a reason beyond my understanding. No matter, certainly some/most(?) 246's are safe with the common NIM standard but relative to my unit, all I can say is, "It's a trap!" (bad reference to a bad Star Wars movie.)

I do like the features on this unit and maybe it is worth trying again. They intend to ohm all the unit's for the 'pin #33' to see if they too are grounded. Again, maybe worth getting and just eliminating that ridiculous ground wire - if that is the case.

As always, thank you Richard for your well researched information and advice.
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Test

1. pull all modules out of the bin
2. replace the fuse
3. plug the bin in and turn it on. all power voltages 12 and 24 should there. If you have a pilot light it should glow..

Bin is in good working order

4. unplug the bin from the wall power outlet. Leave it unplugged for the rest of the tests.
5. put an ohm meter on the ohms range (low 1 ohm range.)
6. firmly connect one lead of the ohmmeter to the case of the power supply or somewhere on the unpainted area of the cage. leave this lead connected for all the rest of the tests.
7. connect the other lead to the AC plug ground lug.
8. this should read near a dead short ground via buss to case and AC plug
9. connecting the free lead of the ohmmeter to either AC plug neutral and hot blades should read open infinite ohms
10. now turn on the power switch
11. both blades should still read open.
12. leave power switch on.
13. put in the TC246 module only!
14. Now read the two blades if any one of them reads zero ohms.......You do indeed have a short within the module to ground.
15. If you read 10 ohms or 20 ohms, you have a bad capacitor or shorted component to ground in the electronics of the module.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Thanks Richard; I will check this out before I get the next amp unit! Then do as you suggest with the amp unit. Still, I'll need to pick up the required fuse - don't have any with the 3 amp value (only higher or much lower values)

A somewhat less expensive Tennelec 246 (that has just 5 pins and no pin at the post #33!) was available so I ordered it. There are some features on the unit that I simply don't follow but thanks for that excellent post on the unit! I now have a somewhat better understanding on some aspects of the unit; however, a lot is still Greek to me but I'm sure that once I start using the unit (if it works!) I will figure it out (I hope ;) ; I did order a service/user manual and hopefully, that clears up any remaining issues (and I don't end up needing the 'service' aspect of the manual!))

So, guess having a pulse generator along with an oscilloscope is essential in order to enable one to test the unit. That will be my next 'learning' experience.
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Re: Question on which NIM amp for a 3He detector?

Post by Rex Allers »

Dennis,

For a better perspective toward us following in the peanut gallery, could you take a picture of the NIM connector on your TC 246 module and post it here.

My curiosity would like to see what pin positions are populated.

As to your fuse, for Richard's measurement suggestions, the unit will be unplugged drawing no current, so any fuse current rating should be fine for this test.

Also, if you remove all the modules, a fuse rated lower than 3 Amp (maybe 1, 1 1/2, 2 would be good) should allow powering up the Bin to measure voltages.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Good points. I do not have the 246 module any more - I sent it back. I did open the unit and a green wire was connected to pin #33 as I posted.

For FYI here is the photo of my NIM box connectors for modules. In the lower, right hand side of the NIM connector are three connectors for module pins: two are for power AC pins - neutral (#41) and Hot (#33). #42 is a ground; possibly the return ground direct to the power cord. The number values printed on the connector are easy to read if you magnify the image.

The upper connectors are the various +/- DC voltage supply connectors and a ground.

The rather large lower pins/connectors are grounding points. I assume the upper two are as well.

I did measure all voltages from the connectors and confirmed that connector #33 is 120 AC; the +/- 6 volt connectors are null, and the +/- 12 & 24 volt DC are all hot and correct. I'll connect the plug and fuse and check the ohm readings on the grounds.
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Re: Question on which NIM amp for a 3He detector?

Post by Rex Allers »

Thanks for the pic. These connectors in the bin have all the asterisked pins in the connector listings and no more. (As one might expect.)

I actually wanted to see a pic of the connector on the back end of the TC 246, though. Assuming you still have it.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

In the previous photo there is a Tennelec 246 but this unit has the normal pin configuration; nothing like the unit I was supplied (still a 246) but that had a ground pin for #33. It had 25 pins on its back and all were wired to the internal circuit board!
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Re: Question on which NIM amp for a 3He detector?

Post by Rex Allers »

So you have already sent back the strange one? That's the one I was hoping to see a pic of its connector.

I believe Richard's testing procedure intended to have that one plugged back in in step 13.

Edit...
Sorry about my reading skills. I just realized you said,
"I do not have the 246 module any more - I sent it back. "

So, I just wanted to apologize for missing that key info.
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Rex is absolutely correct! Without the bad module 246, all my tests are moot.

I deem it insane that all 25 pins on the module's plug were wired to the internal 246 card inside. What the ---- were they doing there? I worry someone had heavily modified the old 246 as an aftermarket non-Tennelec item and that the 33 ground was a very deliberate act.

The big upper and lower pins are merely guide pins and serve no other real purpose. (prevent misalignment and breakage of the tiny pins)
I have seen these guide pins reversed on some modules designed for a custom NIM rack filled with custom modules. Such modules will not mate with a normal NIM rack as the males will jam together and not allow the module to proceed to the plug. Those original NIM spec designers seem to have thought of everything!
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

The new TC 246 arrived today; it has just five pins on its connector and no pin located at position #33, either :) . I placed this unit in the NIM box and did a power check and, of course, nothing at all happened. Which, is for me right now, a good thing.

Also, the pulse generator arrived (later, power loss around here even hit the Post Office. I'm running on a house generator now for a second day.)

As an extreme novice in this area of knowledge, all I can say is I think (dangerous for a novice) I know enough basic stuff to perform the most simple of tests. Hope this isn't too painful for the pro's here.

I first tested the NIM Tennelec 525 rate counter (counts/sec) and it appeared to agree with the pulse generator so that unit seems to be working. Determined its threshold to trip is about 1.0 volt. Not sure if that is normal or an issue. The unit does follow (i.e. counted) 10 Hz to 10,000 Hz accurately on its display scale (using the various base 10 log settings.)

The 246 I am rather ignorant of how to use it. I did apply 50 mV to the input (@ 10000 Hz) and it amplified the output signals on the oscilloscope with each gain setting change. It managed to give 5 volts on its highest gain of 500. That value appears to be off but that might be me. Still, the 246, does appear to be roughly working.

Richard's two pages on the TC 246 that he posted certainly helps but I will need to google a number of terms. Guess when the service/operation manual arrives I can look into the 246's various features in greater detail. This was more a sanity check (of me) just as much as a test of whether these units operate at all.

At some point, I need to do a similar procedure with the pre-amp. That is more a back box to me and I will certainly be asking questions on that unit when I can get to it. This is the same unit Richard mentioned and I assembled (with 3 kV caps.) The board is commercial so definitely more a black box as far as how to properly adjust the amp - and that unit is extremely sensitive (and prone to failure if mis-handled.)
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

I just did a FAQ on setting up an SCA as part of a NIM neutron detection system.

viewtopic.php?t=14550

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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

That is a great addition - thank you Richard!

Of course, I never thought of a gamma source for initial testing. I would think my uranium ore could handle that aspect of the test - though, hardly 'hot'.

The diagram and instructions are very clear and useful. I made a printout as a reference for my 'lab' (along with the NIM pin maps.)

Providing the 'what and why' relative to the devices really does clarify the overall approch. The instructions on use of the oscilloscope is an excellent addition and extremely clear. Especially giving the threshold voltages/expectation values for the detector outputs and the oscilloscope settings is absolutely gold for novices (like me using this type of equipment.) Further, the discussion on the upper/lower 'window' control for the 426 and the principle of setting these controls is clear and explains its purpose and usefulness relative to the detectors.

This FAQ has answered a host of questions I either didn't think of or some I likely would have asked later as I struggled with these devices - really informative.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

A FYI; the Cremat company has a page on testing the touchy CR-110 pre-amp.

https://www.cremat.com/testing-a-csp/

This page assumes one has only the CR-110 'chip'. If one has their circuit board - that unit already has a test connector to interface with the function generator.
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

A question on the TC 246 unit. On the side of the box are switches - do they only apply to their pre-amps or are there specific configurations these should be set for using any general pre-amp?

For instance, I am under the impression that all common coax connectors use 50 ohm. So, the out put should be set to 50 ohm? What use is 1 ohm, then?

Not at all sure what 'shaping' means.

I assume the input polarity is determined by the pre-amp's output signal type?
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

It looks like the output impedance is good at 50 ohms.
You will need to seen what the output pulse polarity is on the preamp using the scope. perhaps you already know it from working with the CR-110
Is the preamp output pulse above or below the zero reference on the scope? The last user, looks as if they chose negative.
The other switch is basically letting you set the output shape and position relative to a baseline or not....
1. Bi-polar (positive and negative levels pass to output). 2. You can also choose unipolar, only outputs a pure positive pulse or negative pulse based on your setting in #1 3. within the unipolar selection you can choose not to have the BLR (Base Line Restorer) active (in) or to let the output pulse fall where it will with reference to your base line (out).

You should play with this module using the scope on the output and a pulse generator or pulser on the input to get a feel for what these switches do. Sadly, you have to slip the module in and out with each change of the switches.

As we are counting only here, I like to go for unipolar, BLR (in)

Have fun and discover much.

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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Thank you again; I realize that discovery is part of the learning experience but after reading both your supplied page (very useful) and the tech manual, those buzz words were still, well not fully clear. The BLR. was a complete mystery. I kinda deduced what pulse shape was (the oscilloscope makes that clear) but why impedance would be changed (kinda know why, now) was a rather strange switch to have but I didn't understand uni-polar or why one would want that feature - till your post.

I did read on the Cremat page that their CSA flip's the polarity of the input signal.

I do enjoy getting to use the oscilloscope but understanding the basics of the switches is extremely helpful.
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

The use of the oscilloscope comes readily with use. The important thing is to get a presentation on the screen that gives the valuable information needed. The main things are to learn how to use the time base knob and channel amplitude knob to get the image contained on screen and to adjust the trigger control to stabilize or lock it in place. Single pulses or irregularly repeated pulses are flawlessly captured and frozen in time with a DSO scope. Virtually 100% of all modern "lunch box scopes" are DSOs. Back in the day a Good DSO Tek scope hit the $5000 price range. A dual channel Saelig of 60 mhz can be had new for under $400 all of these are a DSO. I have seen used ones at hamfests go for $200.

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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

Decided to test the CSA since the TC 426 appeared fine. The CSA appears to work correctly (per the company's overall instructions - apply 1 KHz, about 1 volt pulse to the 'test' connector (not yet marked on my preamp.))

The dual scope mode does appear to match their image but I should have off-set the two signals a bit more. The signal from the pre-amp is from the CR-150's output connection (marked Signal.) The generator pulse input is to the left of that coax connector (unmarked on the preamp box.)

From that source (CSA output sig.) I'm getting the initial response rise from the pre-amp and then a slow decay on the scope. They show it going to zero but I'm no where close to that - maybe my cap is too large(?) I noticed that there really isn't exactly significant amplification (about a 2x factor) by the CSA but it does match up roughly to what the company's pic/value displays (again, minus the decay to zero.)

Guess any significant amplification isn't the primary purpose of a CSA? I was expecting ...well, something more significant, I guess. But then, what do I know about preamps using a CSA?

I 'grounded' each channel to establish a common baseline. No idea if that matters in any way. Playing with the oscilloscope I set the "DC" mode for each channel as well the "AC" mode but both look identical - so, no idea what the significance of those two settings have on the channel/scope relative to this type of test.

Aside: the pulse current that is shown in the company's pic is not displayed on a scope but apparently, they added that as a FYI to their display picture to let you know that the CSA provides a 'current' spike when it see's a signal.

The scope settings were according to the mfg. for testing the CSA. The CSA chip (110) is mounted on their board (CR-150 and enclosed in a metal box with appropriate connectors.) The pulse generator is on top of the oscilloscope and was rather cheap ($30 w/shipping.) It works fine for testing the TC 426, rate meter, and this CSA.

Since I'm still missing a second high voltage cable, using a real detector and with my barely hot ore sample source, may have to wait. Also, I guess I could use the fusor (and may have to) instead of the ore but it is rather short on gamma's but i'd think, could provide some neutrons (33 kV @ 30 ma and 5-8 microns D2).

I might be able to make the extra HV cable I need but that is a bit challenging relative to my skills unless I figure out a work around that doesn't require adding another connector end ;)
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Scope settings (A older, more simple analog scope - easier for me to operate!)
Scope settings (A older, more simple analog scope - easier for me to operate!)
Pulse Generator (Ch. #2) Pre-amp in box to left of scope screen: 1V/div; 1kHz
Pulse Generator (Ch. #2) Pre-amp in box to left of scope screen: 1V/div; 1kHz
CSA Output (Ch. #1) Initial inverted pulse response, then decay till the next (opposite) signal
CSA Output (Ch. #1) Initial inverted pulse response, then decay till the next (opposite) signal
What I got (Ch. #1 & 2) My decay is very slow compared to their diagram
What I got (Ch. #1 & 2) My decay is very slow compared to their diagram
What the company says the preamp output looks like on a scope
What the company says the preamp output looks like on a scope
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

I decided to look at the TC426 amp and see what the various switches on the side do - only the Shaping appears to make a significant difference. The input polarity just reverses the spike direction; the impedance has no effect.

As can be seen in the oscilloscope traces, the shaping switch's two settings change the response pulse from a single spike (unipolar) to a dual response (Bipolar).

The TC426 is set to a gain of just ten. The input pulse is 0.1 volt p-p; again,1 kHz rate. Oscilloscope is 0.1 v/div.

I don't know how one gets along w/o a pulse generator when working with such equipment - and they are so cheap and easy to use now.
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Bipolar: The very narrow bi-polar spike responses are each +/-1.0 volt respectively
Bipolar: The very narrow bi-polar spike responses are each +/-1.0 volt respectively
Unipolar; alternating spike responses from the amp
Unipolar; alternating spike responses from the amp
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

After exploring these features on the TC 426, I tried the window mode (SCA input) but there is no output response when using that input/connection. Not sure if I should bother investigating that problem - I have a service manual and could trace some of the circuit but the unit does basically what I wanted it to do. The issue for me will be getting the detector, preamp and NIM system to work once I have enough HV cables. Whether I can detect neutrons is, apparently, still a remote issue at this point in time. I have no gamma source the fusor will be it when I get to that point.

Wondering if I should install lower cap (but not voltage rating) in the pre-amp? Maybe a faster decay is better?
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Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

For working an SCA you need a very sharp pulse and not a nice square wave or even the classic NIM pulser.

You need a generator that can produce a sharp narrow pulse on the order of 1-2 microseconds width. 5us would do. To test you adjust its amplitude to 1 volt peak on a scope. Feed it to the SCA and set the lower limit to 000 and the upper limit to 000. As the upper limit is advanced you should watch the scope carefully and see the pulse come and go about the 100 point. (assumes 10 volt up/lower range. Some work on a 0-1 volt range.)

All detection pulses in radiation electronics are very fast short pulses. SCAs are built for this and tend not to do well or even work at all with wide fat pulses.

Some also allow for shaping time selection.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Alex Aitken
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Re: Question on which NIM amp for a 3He detector?

Post by Alex Aitken »

Some test inputs are fine with a square wave. They have a capacitor, usually a very small one, in series. This is very common on preamp test inputs, though 1V sounds large for a preamp test pulse. The result is a charge injection/withdrawal on the falling and rising edges of the square wave. Each burst induces a waveform with a shape like a tail pulse. This ought to work just fine as the input to a shaping amplifier. If the output of the shaping amplifier takes a long time to decay, that would suggest something is wrong. I'm not clear on the setup, but the long decay makes me confused. I might be inclined to make sure the input to that is falling fast enough, and check things like impedance if it isn't.
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Richard Hull
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

I speak just to testing the SCA input and discrimination here. Typically the preamp output is simply amplified first to give a very decent signal of a volt or more into the SCA which then tunes out the trash using the SCA. Such signals are typically very narrow pulses.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
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Dennis P Brown
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Re: Question on which NIM amp for a 3He detector?

Post by Dennis P Brown »

My first results with the CSA chip/circuit- where the peak was barely above the curve which did not decrease very much - looks to have turned out to be the fault of the chip rather then due to the larger caps I installed in the board. By the next day the CSA chip's output performance had deteriorate till it was barely responding. Since I was applying all of 2 volts to the test input connector, I seriously doubt my setup harmed it (and I was using their circuit board). So I returned it for a replacement.

The replacement arrived today. Using the new chip in the identical setup the unit now gives the exact response they displayed in the diagram (strong & sharp peak, complete discharge to zero by the end of the square pulse.)

These chips make me nervous because they appear extremely touchy - too bad there is no work-around to avoid them or method that would better protect them. Every time I go to use this pre-amp I am convinced I'll do something wrong and destroy the chip - the last few days haven't made this worry any less.

Speaking of issues with my neutron detector system, one of the my HV coaxial cables had one of its center pins just fall out of its connector! So much for a good solder job by that company (no idea who made it) - this was supplied with my original 3He detector system, no less.

Starting to feel that Lt. Murphy would be interested in my work of late.
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Re: Question on which NIM amp for a 3He detector?

Post by Richard Hull »

Needless to say the input to the CR110 goes to the gate of an FET that has no issue responding to 100 Fa current and is easily destroyed by just clicking on the bias supply. Did we touch on bringing the bias voltage up very slowly and by the same token, lowering it very slowly. The larger the input capacitor value, the more instantaneous pulse current can pass with the instant a 1600 volt bias is just snapped on or off. I usually take about a full minute twirling the ten turn pot on my bias supply from zero to 1600 volts.

My input capacitor in the Princeton Gamma tech preamp is a .002ufd @ 3kv, but I have seen .01ufd caps on PMT preamps. My preamps are discrete component system boards with maybe 50-60 components on the board. (old school)

Richard Hester's fully functional system board used FET input op amp input, but also contained a discriminator circuit as well. He demo'd his board system at one of the early 2000's HEAS. I attach an image of Richard Hester from a 2004 HEAS event. He is a fabulous designer of modern circuitry.
Very missed now but he occasionally checks in here with a post or two.

Richard Hull
Attachments
L to R 2004 HEAS  Richard Hester, Richard Hull, Carl Willis
L to R 2004 HEAS Richard Hester, Richard Hull, Carl Willis
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
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